1. Field of the Invention
The present invention relates to aromatic amine compounds, and light-emitting elements, light-emitting devices, and electronic devices using the aromatic amine compounds.
2. Description of the Related Art
In recent years, research and development have been extensively conducted on light-emitting elements using light-emitting compounds. The light-emitting elements have a basic structure in which a layer containing a light-emitting organic compound is interposed between a pair of electrodes. By applying a voltage to such an element, electrons and holes are injected into the layer containing the light-emitting organic compound from the pair of electrodes, and thus current flows therein. Then, these carriers (electrons and holes) are recombined and thus the light-emitting organic compound is excited. When returning from the excited state to the ground state, the light-emissive organic compound emits light. Because of this mechanism, such a light-emitting element is called a current-excitation light-emitting element.
Such a light-emitting element has a significant advantage in that it can be fabricated to be thin and light because it is formed as an about 0.1-μm-thick organic film, for example. Another advantage is high response speed since the period from carrier injection to light emission is about 1μ second or less. Such advantageous features are effective for flat panel display elements.
Also, because these light-emitting elements are formed as films, planar light emission can be easily obtained by forming a large-area element. On the other hand, point light sources typified by a filament lamp and an LED or linear light sources typified by a fluorescent light do not have the above features; therefore, these light-emitting elements are of value as surface light sources applicable to a lighting device and the like.
Because such a light-emitting element has a number of problems about materials, improvement and development etc., of element structures and materials have been conducted in order to enhance the characteristic thereof.
For example, Non-Patent Document 1 and Patent Document 1 describe light-emitting elements using a blue light-emitting material.
[Patent Document 1]
    Japanese Published Patent Application No. 2007-284431[Non-Patent Document 1]    Meng-Hum Ho, Yao-Shan Wu and Chin H. Chen, 2005 SID International Symposium Digest of Technical Papers, Vol. XXXVI. pp. 802-805.